A fuel cell system including a nitrogen supply unit to a fuel electrode in which nitrogen stored in a liquid nitrogen storage tank is supplied to a fuel electrode of a fuel cell when terminating power generation by a solid oxide fuel cell has been known (refer to Patent Document 1, for example). According to such a fuel cell system, the expansion of nickel and the like used for the fuel electrode, by oxidation when terminating power generation by the solid oxide fuel cell can be prevented in a fuel cell, and, as a result, the damage to an electrolyte composed of a yttria-stabilized zirconia and the like can be avoided.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-220942